No prior art search was conducted on the subject matter of this specification in the U.S. Patent Office or in any other search facility.
We are unaware of any prior art that is relavant to the method of using a catalyst system taught in this specification other than the teachings contained in our own application, Ser. No. 248759, entitled "Palladium Catalyst Promoted By Tungsten," filed on even date herewith. Our other application is assigned to the same assignee as this application and is hereby incorporated by reference. Our other application teaches a specific catalyst system in which a palladium catalyst is promoted by tungsten. The catalyst system has highly desirable characteristics in that it is effective in the catalytic oxidation of unburned hydrocarbons and the catalytic reduction of oxides of nitrogen without significant production of ammonia when an internal combustion engine with which it is associated is operated under fuel rich (oxygen deficient) conditions.
The disclosure of the present specification teaches the use of a catalyst formulation which we also consider to be unique. This unique catalyst formulation contains, on a suitable catalyst substrate, both an upstream catalyst portion containing palladium and a downstream catalyst portion containing palladium and tungsten.
The catalyst formulation set forth in this specification is one which finds utility in several areas. The catalyst system may be used as a three-way catalyst for association with an internal combusion engine which is operated under stoichiometric or slightly fuel rich conditions. The catalyst formulation disclosed is also one which may be used as an oxidation catalyst in association with oxygen rich exhaust gases from an internal combustion engine. Such gases may be developed, for example, by operation of an internal combustion engine under oxygen rich (fuel deficient) conditions. In another case, exhaust gases, though oxygen deficient, may have oxygen added thereto to make the overall gases oxygen rich prior to movement over such an oxidation catalyst. Still another significant use that may be made of this catalyst formulation is in the area of fast burn engines or for engines calibrated from optimum fuel economy emissions standpoint. The same catalyst formulation can be operated fuel rich under high power demand acceleration mode or fuel lean under deceleration or cruise conditions, giving a wide range of flexibility for engine calibration to optimize fuel economy and emissions over a wide range of air/fuel ratios.
The catalyst formulations disclosed herein are based upon palladium and a palladium/tungsten combination. Palladium is a catalyst material which is considerably less expensive than platinum, which has been known in the past for uses in oxidation catalyst systems. Tungsten, of course, is a base metal and is much less expensive than noble metals such as platinum and rhodium.
It is a principal object of the present invention to provide a method of using a low-cost catalyst system which may be used by the catalyst designer in at least three principally different types of catalyst systems. It is a secondary object of this invention to provide a method of using a low-cost catalyst system that functions efficiently in no matter what type of system the catalyst designer has placed the catalyst system.
As is well known to a skilled artisan, an internal combustion engine normally associated with an automobile will generally operate on both sides of a stoichiometric air/fuel ratio during various modes of engine operation. However, the engine designer at the outset of the design of the engine will select an engine operating mode under which the internal combustion engine will normally operate. For example, the so-called fast burn engines currently under development are designed to operate slightly fuel deficient during normal crusing modes of the vehicle. At such time, there is more air present than is required to oxidize the fuel. Therefore, the overall operating mode of the system is oxidizing and the catalyst materials present are operating under oxidizing conditions. In other modes of engine operation, for example, during acceleration periods, internal combustion engines associated with automotive vehicles are normally operated on the rich side of stoichiometry. In this condition, there is more fuel present than air to oxidize the same. In such a case, the overall catalyst system is exposed to reducing conditions because there is not sufficient oxygen available over the catalyst system.
When used with a fast burn internal combustion engine, the catalyst system of the present invention is one which under oxidizing conditions is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and under reducing conditions is effective not only in the catalytic oxidation of unburned hydrocarbons and carbon monoxide, but also in the catalytic reduction of oxides of nitrogen without significant production of ammonia. The catalyst system disclosed in this specification has these excellent characteristics when associated with a fast burn internal combustion engine, even though it uses catalyst materials substantially less expensive than a material such as platinum.
The catalyst system of this invention also has excellent characteristics when used with a slow burn type of internal combustion engine and when used with such an internal combustion engine either as a three-way catalyst or as an oxidation catalyst.